1. Field of the Invention
The present invention relates to adjustable cameras and, more particularly, to pan, tilt, zoom cameras wherein a belt driving the rotational movement of the camera about an axis can be easily and selectively tensioned.
2. Description of the Related Art
Pan-tilt-zoom (PTZ) surveillance camera assemblies commonly use stepper motors to affect the pan and tilt motion of the camera. Such assemblies often include a timing belt operably coupling a small sprocket attached to the motor shaft to a larger sprocket attached to the camera. In operation, the rotation of the motor shaft drives the rotation of the small sprocket. The rotation of the small sprocket, via the belt, affects the rotation of the larger sprocket and, thereby, the movement of the camera. However, tolerances of the camera assembly components may vary from one assembly to the next. Such variances can produce camera assemblies having a belt that is either too loose or too tight. Belts that are too loose may produce hysteresis or slippage that adversely affects preposition accuracy of the camera assembly. Furthermore, a loose belt may shift entirely out of engagement with one or both of the sprockets, thus causing a failure of the assembly. If the belt is too tight, it can be difficult or impossible to assemble and attempts to assemble the belt drive may result in damage to the belt or other components. If assembled, the overly tight belt may induce premature wear of the belt or other components due to excessive forces generated by the overtightened belt.
Some known camera assemblies include a means for selectively adjusting the tension of the belt during assembly to thereby provide the proper belt tension. For instance, dome cameras, available from Bosch Security Systems, Inc. having a place of business at Fairport, N.Y., U.S., are known to use the tilt assembly 10 shown in FIG. 1. The assembly 10 includes a plate 11 having a first opening 12, through which a first rotating member 15 is received, and a second larger opening 13 for receiving a second rotating member (not shown). A motor assembly 14 is engaged to the first rotating member 15 and is mounted to the plate 11 using screws 16, 17. A belt (not shown) operably couples the first rotating member 15 to the second rotating member. To adjust the tension of the belt, the motor assembly 14 is pivoted about pivot screw 16, thus causing the first rotating member 15 to move within first opening 12 and toward or away from second opening 13. Securing screws 17 slide within adjustment slots 18 during pivoting of the motor assembly and are subsequently tightened to secure the motor assembly in position. Although the Bosch dome camera provides an effective means for selectively adjusting the tension of the belt, the use of pivot screw 16 and securing screws 17 presents additional loose hardware that must be assembled.
Pelco dome cameras, available from Pelco, Orangeburg, N.Y., U.S., are known to use the tilt assembly 19 shown in FIG. 2. Tilt assembly 19 includes a plate 20, a motor assembly 21 rotatably mounted in a pocket defined at one end of the plate 20, and a tilt bearing 24 rotatably mounted at the opposite end of the plate 20. A belt (not shown) is positioned on the underside of the plate 20 and connects the rotating members (not shown) of motor assembly 21 and tilt bearing 24. Motor assembly 21 includes an eccentric cam portion 22 and a tab 23. A captive locking screw 25 is provided that engages tab 23. As captive locking screw 25 is adjusted, it moves tab 23 causing motor assembly to rotate within the pocket of plate 20. As the motor assembly 21 rotates in the pocket, eccentric cam portion 22 engages the wall of the pocket causing the motor 21 to move toward or away from the tilt bearing 24, thereby tightening the belt.
Although the known systems provide for the selective tensioning of a belt drive system for a PTZ camera, an improved assembly is desirable.